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Thread: Significant figures problems.

  1. #1 Significant figures problems. 
    Forum Freshman
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    Hi everything,

    Don't worry I know how the significant figures work. However, I don't know how to use the rule here :

    [(81.35 ml -81.321 ml)/ 81.321 ml ] * 100 = ?

    Thanks.


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  3. #2  
    Forum Masters Degree organic god's Avatar
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    i take it this is some kind of percentage difference question?

    In my opinion the least accurate number given is 81.35 so this is the most significant figures you can use. the 100 is just to make it into a percentage right?


    everything is mathematical.
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  4. #3  
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    Its true that the most inaccurate number you have is 81.35 because it could be anything from 81.345 to 81.3549. However, if you have a more accurate number I would always advise it's use as more accuracy can never hurt anybody!

    When you crunch these numbers as you've entered them, you get the answer of 0.035661145etc which can be expressed as 0.04 to 1SF, or as 0.036 to 2SF, or as 0.0357 to 3SF

    Each of these answers is correct it just depends on what level of accuracy you need. If youre filling a 20L conical flask the 0.003ml will make no difference, but if youre flask is 0.006ml, then your value suddenly has more meaning.

    I just dont quite understand your question
    Chemistry is everything!
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  5. #4  
    Forum Masters Degree organic god's Avatar
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    I'm not sure I agree with you Luka, if the measurement as 81.35 including any more numbers in the final measurement is ridiculous as you cant have any confidence in the accuracy of the final answer
    everything is mathematical.
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  6. #5  
    Reptile Dysfunction drowsy turtle's Avatar
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    You would surely make your answer precise to a number of decimal places? (before multiplying by 100 of course);

    e.g.

    If you keep to the same number of significant figures in the answer as used to calculate it, your answer would be 1.01, whereas you can safely assume that your answer is accurate to the nearest because that is the accuracy of the original values you used.


    Let's say you are working out the voltage in a component;



    I=0.56
    R=1.789

    Because the least accurate value is accurate to only 2 decimal places, you would express the answer to 2 decimal places also.

    so;


    to 2 decimal places.


    Strange that it happened to equal 1.00 - not intentional at all, just random numbers!
    "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." ~ Douglas Adams
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